The present invention relates to a rolling piston type rotary machine operable as a vacuum pump which provides a vacuum source either to be installed in an automobile equipped with a Diesel engine or to be used as a brake booster of a vehicle.
In the conventional rolling piston type rotary machine, suction and discharge ports are formed in a cylinder on the opposite sides of a vane. When a rotor is brought to a position in which the point of contact between the outer surface of the rotor and the inner peripheral surface of the cylinder is positioned between the suction and discharge ports, the suction and discharge ports are communicated with each other through a crescent-shaped space defined between the rotor and the cylinder and positioned at this moment at a place remote from the vane. In the case where the rotor is revolved at a high speed, there is a possibility that a check valve is not operative to follow the high speed revolution of the rotor, with a resultant disadvantage that the check valve fails to sufficiently seal a discharge port against the atmospheric pressure. In such an event, the atmospheric air flows through the discharge port back into the space between the rotor and the cylinder. In consequence, the machine produces noise, requires an increased magnitude of driving torque and creates a lowered level of vacuum. The present invention has its object to eliminate the communication between the suction and discharge ports which is caused in the prior art due to the failure of the check valve operation.